すみません、宅急便の荷物を受け取りたいのですが。 — Excuse me, I'd like to pick up a delivery package (Takkyubin). (Convenience · Store · Service, Formal — to staff, JLPT N5)

Gesture & etiquette

Hold out hands as if to receive something, or show a notification on a phone if applicable.

You will need either a tracking number, a specific pickup code (if sent to a locker/pickup point), or ID matching the recipient name. Make sure you know which delivery service (Yamato, Sagawa, Japan Post) was used.